Benthic algae are a major source of carbon supporting aquatic food webs in northern Australia, but little is known about the factors that regulate algal production. We surveyed benthic algal biomass in mainstem habitats of an unregulated sandy tropical river (the Fitzroy River) during a base-flow period. We used predictive models to reveal the physical and chemical parameters controlling algal biomass in mainstem habitats. We found that water velocity was an important driver—algal biomass was lower at higher water velocities. Subsurface flow was also influential—algal biomass increased in locations where groundwater upwelling occurred, as evident by a positive relationship between algal biomass and elevated radon and ammonium concentrations. In this sand-bed river, it is likely that high water velocity destabilises the sandy substrate reducing the establishment of algal biofilms. However, where water velocity is low enough for algal establishment, groundwater upwelling likely promotes algal growth by delivering limiting resources and/or creating stable conditions that promote algal production. The importance of surface and subsurface-flow conditions to benthic algal biomass means that any modification to the Fitzroy River catchment that alters dry-season longitudinal flows (via river regulation) or groundwater levels (via groundwater extraction) may directly influence river algal production.

中文翻译：

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水流速度和地下水上升流影响热带含沙河流中的底栖藻类生物量：对水资源开发的影响

底栖藻类是澳大利亚北部支持水生食物网的主要碳来源，但对调节藻类生产的因素知之甚少。我们在基流期间调查了一条不受管制的热带沙河（菲茨罗伊河）的主要栖息地中的底栖藻类生物量。我们使用预测模型来揭示控制主要栖息地藻类生物量的物理和化学参数。我们发现水流速度是一个重要的驱动因素——藻类生物量在较高的水流速度下较低。地下水流也有影响——藻类生物量在发生地下水上升流的地方增加，这可以从藻类生物量与氡和铵浓度升高之间的正相关关系中看出。在这条沙河中，高水速很可能会破坏沙质基质，从而减少藻类生物膜的形成。然而，在水流速度足够低的情况下，地下水上升可能会通过提供有限的资源和/或创造促进藻类生产的稳定条件来促进藻类生长。地表和地下流条件对底栖藻类生物量的重要性意味着，任何改变干季纵向流量（通过河流调节）或地下水位（通过地下水提取）的菲茨罗伊河集水区的改造都可能直接影响河藻生产。地下水上升可能通过提供有限的资源和/或创造促进藻类生产的稳定条件来促进藻类生长。地表和地下流条件对底栖藻类生物量的重要性意味着，任何改变干季纵向流量（通过河流调节）或地下水位（通过地下水提取）的菲茨罗伊河集水区的改造都可能直接影响河藻生产。地下水上升可能通过提供有限的资源和/或创造促进藻类生产的稳定条件来促进藻类生长。地表和地下水流条件对底栖藻类生物量的重要性意味着，对菲茨罗伊河集水区进行的任何改变旱季纵向流量（通过河流调节）或地下水位（通过地下水提取）的改造都可能直接影响河藻生产。